The present invention relates to a developer for a presensitized plate (hereunder referred to as "PS plate requiring no dampening water") for use in making a lithographic printing plate which does not require dampening water during printing and which comprises a silicone rubber layer serving as an ink repellent layer (hereunder referred to as "lithographic plate requiring no dampening water") and in particular to a developer for a PS plate requiring no dampening water which is excellent in particular in developing ability and half tone dot reproduction and which hardly causes foaming.
There have already been proposed a variety of PS plates requiring no dampening water which comprise, as an ink repellent layer, a silicone rubber layer. Among these, particularly preferred are those comprising a substrate provided thereon with, in order, a light-sensitive resin layer and a silicone rubber layer, specific examples of which are those disclosed in, for instance, Japanese Patent Publication for Opposition Purpose (hereinafter referred to as "J.P. KOKOKO") Nos. Sho 54-26923 (U.S. Pat. No. 3,894,873) and Sho 55-22781 (Brit. Pat. 1,419,643).
These PS plates requiring no dampening water can be roughly divided into two groups, one of which are those disclosed in, for instance, J.P. KOKOKU Nos. Sho 42-21879, Sho 46-16044(U.S. Pat. No. 3,511, 178) and Sho 55-22781 and Japanese Patent Unexamined Publication (hereunder referred to as "J.P. KOKAI") Nos. 49-86103 and Sho 49-68803 and whose non-exposed portions (image areas) are dissolved by a developer and in which the silicone rubber layer on the image areas is accordingly removed and the other of which are those disclosed in, for instance, J.P. KOKOKU Nos. Sho 54-26923, Sho 56-23150 and Sho 56-12861 and whose exposed portions (non-image areas) are firmly adhered to the light-sensitive layer through photoadhesion and in which only the silicone rubber layer on the non-exposed portions (image areas) is removed by the action of an organic solvent capable of swelling only the silicone rubber layer on the non-exposed areas.
Though these PS plate requiring no dampening water can be developed with an appropriate organic solvent, developers mainly comprising water have been proposed for eliminating any possibility of firing (see, for instance, J.P. KOKAI No. Hei 1-159644 (U.S. Pat. No. 4,959,296) and Japanese Patent Application Serial (hereunder referred to as "J.P A.") No. Hei 1-139558(EP 0400657A)).
However, these developers mainly comprising water are those obtained by dissolving a solvent hardly soluble in water with the aid of a surfactant and correspondingly they cause foaming during developing operations. Thus, if they are used in an automatic developing machine, the solution overflows from a tank due to the foaming. Moreover, the surfactant does not swell or dissolve a light-sensitive layer at all, accordingly the developing ability of the developer is not improved by the addition of a surfactant and the addition thereof simply leads to the reduction in the water content. Therefore, the developing ability thereof is not good although water content is rather high.